Wavefront-guide technology, or customized vision correction, is becoming a new frontier for vision and ophthalmology because it offers the capability to manipulate high-order aberrations in the eye. There are fundamentally two kinds of wavefront customizations: supernormal vision corrections that allow the correction of high-order aberrations in an eye and presbyopic corrections that increase focus depth of an eye by introducing certain high-order aberrations.
Supernormal vision corrections were first obtained in laboratories using a technology called adaptive optics, as disclosed in “Supernormal vision and high resolution retinal imaging through adaptive optics,” J. Opt. Soc. Am. A, vol. 14, pp2884-2892 by Liang, Williams and Miller in 1997, and in U.S. Pat. No. 5,777,719, issued Jul. 7, 1998 by Williams and Liang. Since the first demonstration of supernormal vision with adaptive optics, extensive efforts have been made recently in the filed of laser vision correction as described in “Aberration-Free Refractive Surgeries,” Springer-Verlag, 2003, Bille et al ed., and in “Wavefront Customized Visual Correction: The Quest for Super Vision II,”, Slack Inc, 2004, Krueger et al ed.
An ultimate goal for a supernormal vision correction has been to create an aberration-free eye. FIG. 1 shows the Modulation-Transfer Functions (MTF) and simulated retinal images of an acuity chart for an aberration-free eye in three viewing distances. FIG. 1a and FIG. 1b show a Modulation-Transfer Function (MTF) and simulated retinal images of an acuity chart for an aberration-free eye at the best focus. We assume the aberration-free eye is refracted to have the best focus 6 meters away from the eye, matching to the situation in a conventional subjective refraction. Because human eyes must function for a range of focus depth, we also show MTFs and retinal images of the same aberration-free eye at 3 meters (a focus shift of 0.17 Dioptors) in FIG. 1c and FIG. 1d, and at 30 meters (a focus shift of 0.13 Dioptors) in FIG. 1e and FIG. 1f. Two important aspects are clearly seen for the aberration-free eye. First, the aberration-free eye has extremely clear vision at the best focus, shown in the retinal images as well as in MTF at the high frequency around 60 c/deg. Second, the aberration-free eye is extremely sensitive to a focus offset, even as small as 0.1 Dioptors.
One should re-consider the creation of aberration-free eyes for at least two reasons. First, an aberration-free eye can only see clearly at the exact focus position; and a slight shift of focus (about 0.1 Dioptors) will make vision of the eye totally blurred. Second, at the exact focus position with superior clarity, the aberration-free eye won't be good for all vision tasks, in particular for high frequency structures. Improved image quality with an aberration-free optics could cause mismatches between aberration-free optics of the eye and the retinal sampling by photoreceptors. It is possible that aliasing may happen for high-frequency features and distort vision as described in “Aliasing in human foveal vision” Vision Research, vol. 25, pp195-205 by D R Williams in 1985.
Wavefront customizations also include presbyopic treatments for elderly eyes. Certain high-order aberrations such as spherical aberration can be introduced into elderly eyes for increased focus depth. However, increasing focus depth must come at a cost of reduced image quality. If not controlled properly, the introduced high-order aberrations will not only reduced image contrast, but also cause unwanted vision symptoms such as glare, halo, and starburst.
Wavefront technology not only offers advantages for altering high-order aberrations in the eye, but also poses challenges to design, evaluation and specification of wavefront-guided vision correction. Improper wavefront corrections can cause harms to vision rather than improve vision quality.
In light of the forgoing, it is readily apparent that a need exists in the art to provide a comprehensive vision architectures for designing, specifying and diagnosing wavefront-guided vision corrections. The comprehensive architecture must contain a more reasonable performance target than an aberration-free eye, enable to predict vision quality from wave aberration in the eye, and include features to prevent vision symptoms such as glare, halo, starburst, and ghost images.
An additional need also exists in the art to provide methods to specify wavefront-guided vision correction beyond visual acuity, because good acuity is a necessary but not a sufficient condition for excellent vision. With introduction of new products based on new procedures, new materials, and new correction forms, specifying vision quality beyond visual acuity is necessary to prevent potentially inferior products with night vision symptoms, insufficient vision clarity and insufficient focus depth.